The gene encoding an enzyme called homogentisate 1,2-dioxygenase
(also known as homogentisate oxidase). HGD is located on chromosome 3 in region
3q21-q23.
H omogentisate oxidase is active chiefly in the liver and kidneys. It is needed
to break down the amino acids phenylalanine and tyrosine. Previous steps convert
these two amino acids into a molecule called homogentisic acid. Homogentisate oxidase
adds two oxygen atoms to homogentisic acid, converting it to another molecule called
maleylacetoacetate. Other enzymes break down maleylacetoacetate into smaller molecules
that are later used for energy or to make other products that can be used by the
body.
More than 40 mutations in the HGD gene have been identified in people with alkaptonuria.
Many of these mutations change single amino acids in the homogentisate oxidase protein.
For example, a substitution of the amino acid valine for methionine at position
368 (also written as Met368Val) is the most common HGD mutation in European populations.
Mutations in the HGD gene probably inactivate the enzyme by changing its structure.
Without active homogentisate oxidase, homogentisic acid builds up in the body. It
is deposited in connective tissues such as cartilage and skin, causing them to darken
and leading to arthritis. Homogentisic acid is also present in urine, causing the
urine to turn black when exposed to air.
medical
dictionary, online medical dictionary, medical
terminology dictionary, free online medical
dictionary, medical dictionary, online medical
dictionary, medical terminology dictionary, free
online medical dictionary, dictionary medical,
dictionary medical online, dictionary medical
terminology, dictionary free medical online,
dictionary free medical, dictionary medical
terms, dictionary drug medical medicine,
dictionary health illustrated medical nursing
profession stedmans, dictionary English medical,
dictionary medical online terminology,
dictionary encyclopedia medical online,
condition dictionary medical, dictionary
medical, dictionary drug medical, medical
dictionary software, cyclopedic dictionary index
medical tabers thumb, medical dictionary, online
medical dictionary, medical terminology
dictionary
